The Global Positioning System (GPS) or another global navigation satellite system (GNSS) provides location information to a receiving device anywhere on Earth as long as the device has a substantial line of sight without significant obstruction to three or four satellites of the system. The GPS system is maintained and made available by the United States government. Originally, the government retained exclusive use of GPS. Over time increasing levels of accuracy of the GPS signals were made available to the public.
Accuracy of the GPS system alone is about 50 feet or 15 meters. The accuracy may be augmented using secondary techniques or systems such as the Wide Area Augmentation System (WAAS), Differential GPS (DGPS), inertial navigation systems (INS) and Assisted GPS. WAAS and DGPS improve accuracy using ground stations that transmit position information. INS utilizes internal sensors at the receiving device for improving the accuracy of GPS.
However, some applications require greater accuracies obtainable with GPS, even with enhanced accuracy techniques. For example, in high definition mapping and navigating application, the receiving device may be placed on a map in a three-dimensional view with greater accuracy than that obtainable from GPS techniques. Localization techniques that match a location to a map or environment face additional challenging in improving this accuracy.